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Mental Illness and Violence: A Link?

Mental Illness Alone Doesn't Predict Violence, but Substance Abuse Increases Risk for Mentally Ill, Study Shows
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 2, 2009 -- When horrific acts of violence erupt, such as killing rampages on school campuses or mass slayings by heads of families, the public often reacts by saying the offender must have been "crazy."

Although mental illness and violence are often thought by society to go together, the perception is not entirely true, according to a new study.

"Mental illness alone does not increase the risk of violence," says Eric Elbogen, PhD, assistant professor of psychiatry at the University of North Carolina at Chapel Hill School of Medicine, citing the results of his recent study published in the Archives of General Psychiatry.

But when mental illness is combined with other risk factors such as substance abuse, it does increase the risk of violence, Elbogen found. Mental illness "makes a difference but only in the presence of other risk factors," he says. Besides substance abuse, Elbogen looked at such other factors such as a history of violence, age, gender, and stressors such as losing a job or getting a divorce.

Mental Illness & Violence: The Study

Previous research has produced mixed results about the link between mental illness and violence, with some finding a clear association and other studies finding, as did Elbogen's, that alcohol and drug abuse increases the risk in the presence of a mental illness.

For his study, Elbogen evaluated data on nearly 35,000 people, all interviewed about their mental health, history of violence, and use of substances between 2001 and 2003. Participants were part of the National Epidemiological Survey on Alcohol and Related Conditions, conducted by the National Institute on Alcohol Abuse and Alcoholism.

At the first interview:

  • Nearly 11% of participants said they had been diagnosed with mental illness, including schizophrenia, bipolar disorder, or major depression.
  •  21.4% had substance abuse or substance dependence.
  •  9.4% reported a severe mental disorder and substance abuse or dependence.

The percentage of participants reporting a mental illness reflects the percentages found in the general population and in other studies, Elbogen says.

In a second interview conducted in 2004 or 2005, participants were asked about any violent behavior, such as committing a sexual assault, fighting, or setting fires, in the time between interviews.

Mental Illness & Violence: Results

In all, 2.9% of participants said they had been violent in the time between the first and second interviews.

When Elbogen evaluated the possible associations between mental illness, violence, and other factors, having a mental illness alone did not predict violence, but having a mental illness and a substance abuse problem did increase the risk of violence.

The risk was increased even more if the person had mental illness, substance abuse problems, and a history of violence.

For instance, when Elbogen looked at those who only had a severe mental illness, 2.4% had been violent. But when he looked at those with major depression and substance abuse or dependence, 6.47% had been violent.

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